Precision potentiometer



Jan. 29, 1963 R. E. cHARLl-:s

PRECISION POTENTIOMETER Filed Feb. s, 1961 9 3 t W kr K d f r m-\ Q\ *N QN W w. mww E Mu w M fl Nm I Wm. .VG WW x k om. Lmw, Q 1,. h ON No HV .=w\ h. qm 3 -u||| R o om Hmm f wa f .Nm F v I 7 z i l Qm .H Lim om E Nm I I o .mu u.. Nm

United States Patent O 3,h76,161 PRECESEN PStENTHft/EETER Randolph E. Charles, Wayland, Mass. {4 Gordon t. (Room 112), Walthers: 54, Mass.) Filed Feh. 3, 1961, Ser. No. ffiytl 4 Claims. (Cl. S-Stll) This invention relates to electrical current regulating devices and more particularly to devices for varying the resistance in an electric Circuit. Such devices are commonly called potentiometers.

'Ihe usual potentiometer consists in essence of a first element of relatively high resistance which is contacted slidably by a second elernent. The two elements are connected in series in the circuit, the first element being disposed in such manner that as the second element slides along the first element the electrical current must pass through an increasingly larger segment of the first element, thereby increasing the resistance in the Circuit. The configuration of the first element is usually a high resistance wire wound on a core of insulating material Which generally is fiat or Circular.

Regardless of the configuration of the resistance element, the prior art potentiometers have always include someplace in the Circuit engaging elements which slide with respect to each other. By its very nature, a sliding contact creates electrical noise, and this noise produces an adverse effect on the operation of the circuit.

Another disadvantage in sliding contact devices is found in the Wear which the sliding contact causes on the resistance element. Where a resistance Wire is Wouud spirally around a base or core, the pressure of the sliding contact thereon coupled with the friction of its sliding causes a high rate of wear.

Accordingly, it is an object of my inven'tion to provide a potentiometer in Which there is no loss of accuracy or usefulness due to contact noise or sliding friction.

It is another object of my invention to provide a potentiorneter in which the resistance element will subjected to a minimum of forces which tend to cause it to wear out, as, for example, by sliding the contact over it. I lt is a further object of my invention to provide a potentiometer in which the path of the electrical current at no point passes through a sliding connection.

ln the practice of my invention in a preferred cmbodiment thereof, I construct a potentiometer having two rings of equal interior radius mounted coaxially. One ring serves as a commutator and the other is wound With 'resistance wire and serves as the resistance element. A one-piece roller, with its ends engaging the interior surfaces of the commutator and resistance wire, is disposed on a spring loaded arm extending transversely of the two rings and serves as the contact member. The roller cas'rying arm is positioned on a shaft wherehy it may be caused to move the roller around the inside face of the two rings. As the roller is rolled away from the beginning of the resistance element, the resistance in the Circuit is increased.

it is a feature of my invcntion that the current fiow through the Commutator, roller and resistance element is accomplished without its passing through any sliding contact.

it is another feature of my invention that the roller engages the resistance element ring in a substantiaily frictionless contact.

lt is a further feature of my invention that substantially greater pressure than has heretofo-re been feasible may be employed to engage the roller with the resistance ring while at the same time the useful life of the sistance wire is substantially increased.

These and other objects and features of my invention Fatented Jan. 29, l

m, will appear as the description proceeds with the aid of the accompanying drawings, in which:

FlG. 1 is a sectional view of a potentio-meter accor 1- ing to my invention taken along the line l-ll of FEG 2;

FIG. 2 is a section along the line 2-2 of l;

FIG. 3 is a fragmentary section along the line 3-3 of FIG. Z; and

FiG. 4 is a diagrammatic exposition of my invention.

Referring to FIG. 4 for an explanation of the theory of my invention, a commutator bar lit is shown having a lead wire 12; whoreby it may be connected into an appropriate electric circuit (not shown). ln spaced parallel relation to the commutstor is positioned a resistance element indicated at M. The resistance element 14 Comprises an insulated bar 16 around which a resistance wire 18 is wound. A contact member indicated at 2G is positioned to eneage the commutator lf; resistance element 14- and comprises a center shaft 22 of any suitable diameter and roller wheels 24; lilrewise of any suitable diameter which are formed. integrally With the shaft 22. it is obvious that the contact member may be rolled substantially without friction along the commutator 1G and resistance element lll, thereby verying the resistance in the Circuit.

Refcrring now to FIGS. l, 2 and 3 for a more particular description of a preferred enibodiment of my invention, l provide a housing indicated at which may be Constructed of any suitable material and need not hc electrically non-conductive. ln practice, the housing has a cylindrical wall ZS and a fiat Circular end wall Ei).

Within the housing, I position a first insulating sleeve 32 Which engages the housing 26 snugly and fits against the end wall h. The purpose of the insulating sleeve 32 is to electrically insulate the housing 26 from a resistance element indicated at 34. The resistance element 2:4 comprises a sleeve of insulating material 35 around Which a resistance wire 38 is wound, each turn spaced yrom the next. The sleeve 34 extends around the insulating sleeve 32 for nearly the entire circumference. An end till of the wire 38 passes through a short insulatmember 4-2 to the outside of the housing Zo where it terminates in a binding post 4-47.

A second insulating sleeve 46 is positioned snugly within the housing 26 parallel to and spaced apart from the insulating sleeve 32, and a Circular comn: tatcr d is positioned within it. The Commutator d is connected to a wire t) which passes through an insulating member 52 to the outside of the housing Ze Where it terminates in a binding post In order to provide means for engaging the commutator 4-3 and resistance element 34, a central shaft 55 is first positioned extending along the common axis the-reor". This is accomplished by providing a short cyllndrical hearing 58 extending inwardly from the end wall and dimensioned to engage one end of the shaft The other end of the shaft 56 passes through a hearing of.) formed in a cover 62 Which completes the housing The shaft So is thus rotatably positioned in the hearrings 58 and till. A andle 62 is provided for rotating the shaft 56.

Positioned on shaft Se is an arm 54 which at one end is divided -as at de Whereby it may be Clamped on shaft 5:5 hy a bolt s. An electrically non-conductive bushing o'? is positioned between the arm 64 and shaft 55 to prevent any electrical current in the yarm 54 from passing to the shaft 56. The farm 613 is formed at one end into a forl: indicated at iii (see HG. 3) and having spaced side elements 59 .and 71.

A rocker arm 72 is pivotally disposed in the fork 76 on a pivot member '74 which is niounted through the elements d and fil. An end 76 of the rocker arm 72 eX- antalet '2 a tends beyond the fork 'Til and is attached to a coiled tension spring '73. The spring 7 8 is also attached to the arm 64 land tends to pull the end 76 toward the arm 64. The opposite end 8% of the rocker'arm 72. likewise extends beyond the fork 'it and is formed to receive the outer race 32 of a ball hearing in which the inner race is indicated at 36 and -the ball at 344. Inner race Sd is firrnly engaged on the shaft segment 38 of a contact member indicated at Stil.

The contact 9% comprises a roller or dumbbell Shaped member having shaft d and rolling se-gments 2 and 93. The contact 9% is dimensioned so that one end 92 will travel over the commutator d and the other end 93 over the wires 38 of resistance element 34. Contact Mt is of unitary construction and is made of anyv suitable materiai of good electrical conductivity.

The operation of my invention is as follows: The potentiometer is connected into the desired electrical circuit through binding posts 44 Iand 54. The current in the cir-cuit then fiows through commutator 43, cont-act hd and resistance element 34. By rotation of handle 62, the position of contact 9G on resistance element M'may be changed, therehy changing the -over-all resistance of the unit. lt will be noted that at no point does the current flow through a sliding connection. End elements 92 and 93 of contact 9% are of the same diameter, are integral with shaft 83 thereof and rotate with relation to oommutator s and resistance element 34, which also are of the same internal diameter. Since the contact is rolling, not sliding, the resistance wire 38 may be o-f very fine fabrication and the pressure of end segments 192 and 93 against resistance element 94% may safely be substantially greater than would be possible with a sliding contact.

I-t should be taot noise to an extremely sliding contact.

It is my intention to clairn all changes and modifications of the preferred einbodiment of my invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

I clairn:

1. A potentiometer comprising a base, -a first insulating sleeve mounted on said base, la commutator comprising a sleeve of electrically conductive material having a low resistance mounted within said first insulating sleeve, a second insulating sleeve mounted on said base parallel to said first insulating sleevc, a resistance element comprising an insulating core having a wire of high resist- -ance Wound therearound positioned within said second insulating sleeve and being of equal interior radius and coaxial with said commutator, rolling means for making an electrical contact between said commutator and said resistance element, means for moving said rolling means noted that my construction reduces conlow level by eliminating any [i around said -commutator and said resistance element in a circular path coaxial with said commutator and resistance element and inside thereof, and means for urging said rolling means firmly against said commutator and resistance element.

2. A potentiometer as dened in claim 1, further charaeterized -by said rolling means comprising a shaft positioned by said moving means parallel to the coin-mon axis of said commutator and said resistance element, end segments on said shaf-t and integral therewith and having a substantially cylindrical configuration and engaged on said commutator and said resistance element with the axl-s of said cylindrical end segments common with the axis of the said shaft.

3. A potentiometer as defined in clairn 1, further characterized by said means for moving said rolling means comprising a shaft rotatably disposed on said base along the axis of said comm-utator and said resistance element, a first arm releasably engaged on'said shaft, means for insulating said arm electrically vfrom said shaft, said means for urging said rolling means against said commutator and resistance element icomprising la fork formed at the router end of said arm, a second arm pivotally dis- -posed in said forlr element, a first end on said second arm extending beyond said fork element, a coiled spring connected to said first end of said second arm and to said first arm to draw said first end downwardly toward said shat't, a second end on said second arm extending beyond said fork element and'opposite to said first end thereof, a ball hearing positioned in said second end of said second arm having an outer race engaged therewith and an inner race for receiving the said contact making rolling means.

4. A potentiorneter comprising a circular insulating core having -a resistance wire wound thereon, a circular commutator having [the same inside diameter as said resistance wire covered core, said core and commutator being parallel and coaxial, said core and commutator having means vat their one end-s for connecting them into a circuit, a roller Contacting element having end portions of the same diameter, one end portion engaging the resistance wire yand the other end portion engaging the cornmutator, means for causing said contacting element to roll about the interiors of said resistance wire and commutator, whereby the resistance in said circuit may be varied, and means for holding said Contacting element against said resistance wire and commutator wit-h a substantially constant pressure.

References Cited in the file of this patent UNITED STATES PATENTS 2,368,710 Hessey Feb. 6, 1945 2,476,799 Berthiez July 19, 1949 1833309 Mariotti'et al. May 6, 1958 

1. A POTENTIOMETER COMPRISING A BASE, A FIRST INSULATING SLEEVE MOUNTED ON SAID BASE, A COMMUTATOR COMPRISING A SLEEVE OF ELECTRICALLY CONDUCTIVE MATERIAL HAVING A LOW RESISTANCE MOUNTED WITHIN SAID FIRST INSULATING SLEEVE, A SECOND INSULATING SLEEVE MOUNTED ON SAID BASE PARALLEL TO SAID FIRST INSULATING SLEEVE, A RESISTANCE ELEMENT COMPRISING AN INSULATING CORE HAVING A WIRE OF HIGH RESISTANCE WOUND THEREAROUND POSITIONED WITHIN SAID SECOND INSULATING SLEEVE AND BEING OF EQUAL INTERIOR RADIUS AND COAXIAL WITH SAID COMMUTATOR, ROLLING MEANS FOR MAKING AN ELECTRICAL CONTACT BETWEEN SAID COMMUTATOR AND SAID RESISTANCE ELEMENT, MEANS FOR MOVING SAID ROLLING MEANS AROUND SAID COMMUTATOR AND SAID RESISTANCE ELEMENT IN A CIRCULAR PATH COAXIAL WITH SAID COMMUTATOR AND RESISTANCE ELEMENT AND INSIDE THEREOF, AND MEANS FOR URGING SAID ROLLING MEANS FIRMLY AGAINST SAID COMMUTATOR AND RESISTANCE ELEMENT. 